Gas turbine engine airfoils are often conventionally formed around a casting core during an investment casting process. In order to form an airfoil with multiple walls, two or more casting cores are separately formed and then secured so they form a two-piece core assembly suitable for use in the investment casting process. However, this process may result in airfoil walls that do not meet dimensional tolerances due to mismatch during the assembly of the casting cores, due to relative movement of the casting cores during the casting process, and due to the two-piece core assembly shifting in-place during the casting process. Consequently, there remains room in the art for improvement.